The present invention is directed to novel methods and apparatus for controlling the population of fish, aquatic mammals, and the like in a defined area of a body of water.
It is known that sound and other stimuli can cause voluntary and involuntary movement in marine and aquatic creatures. It has heretofore been suggested that sonic waves could be utilized to drive fish away from water intakes, and to attract fish into areas where they could be netted. However, so far as is known, such procedures have not proven effective because different species of fish will respond differently to the same stimuli, and the same species may respond differently to the same stimulus under different environmental conditions, e.g., water temperature, time of day, etc.
It will be appreciated that effective use of stimuli to control marine population is a given area of a body of water could have constructive, protective applications by deterring marine and aquatic organisms from dangerous or undesirable areas, such as water intakes and sites of chemical discharges, or by attracting them to more desirable areas such as fish ladders and bypasses around water intakes.
As used herein, the term "marine creatures" or "marine species" refers to fish, crustaceans, and other non-mammalian species which are resident in water and which are self-propelling and responsive to external stimuli. The term "aquatic creature" or "aquatic species" refers to mammals which reside in the water such as dolphins, seals, manatees and sea lions, and to birds and other animals which swim and dive below the surface of the water such as beavers, and muskrats.
As used herein, the term "stimuli" is intended to encompass a single stimulus and multiple stimuli, whether sequentially or simultaneously generated, and which may have the effect of attracting or repelling a subject species.
Sensitivity to potential stimuli such as sound, light, heat, and chemicals is species-specific and depends on biological form, structure, and function. Less well known are animal sensitivities to magnetism, electrical fields, radio frequency waves, and gravity. For a single species, sensitivity to a given stimulus may be affected by environment, instinct, conditioning, or unknown factors. The response of a subject species to a stimulus which it senses may also be dependent on these factors. Does the subject species sense the stimulus as an irritant, a noise (referring to background or interfering levels of the stimulus), or a signal. If it is interpreted as a signal, does the species consider it to signify danger, safety, food, a predator, or something else? Observable animal responses to stimuli include startle (a sudden, but not necessarily directional movement); avoidance (motion away from the source); and attraction (motion toward the source). As the ability to accurately generate and detect species response to stimuli increases, the ability to use these stimuli to constructively influence the movement of marine and aquatic species is increased.
A stimulus that generates a response during daylight may be ineffective at night. An effective stimulus or pattern of stimuli which is repeated may become ineffective if the subject becomes acclimated to it. A stimulus that is too strong may disorient the subject species or incapacitate it. Some species may be unable to discern a sonic stimulus which is below the level of background noise; additionally, levels of background noise fluctuate, requiring changes in relative and absolute signal strength.
Attempts to influence the behavior of marine and aquatic organisms such as fish by use of acoustic, photic, electrical, and mechanical energy have been pursued in the past. Many of the devices used to produce underwater sound employed mechanical or electromechanical sources such as bells, chains, drums, pipes, plates, or pneumatic "poppers". Other devices have employed electrical sources of sound, such as audiomagnetic tape players connected to underwater speakers or simple signal oscillators and transducers. Usually, these devices were employed to transmit sounds which were intended to irritate fish.
In some cases, investigators seeking to repel fish selected a sound which they, as humans, found annoying. In one case, the sounds included "rock music" and the sound of a "video arcade game"; the investigators apparently assumed that the fish would also find these sounds annoying. These well-intending, somewhat anthropomorphic efforts reflect neither the current state of the art in underwater signal generation nor consideration of the sensory perception of individual marine and aquatic species. If these sounds are at all detectable by fish, there is a logical probability that some species will be attracted by the sounds, that some will find them repulsive, and that some will ignore them. These acoustic efforts are probably indicative of efforts to attract or repel fish using other forms of energy as well.
More recently, the effects of discrete acoustic signals (used alone or in combination with lights or other stimuli) on individual fish species have been studied. While this research indicates that the behavior of some species of fish and aquatic mammals can be influenced by certain sounds, the results are not comprehensive and are of inconclusive value in field applications. These studies did not employ high sound source levels (more than 180 decibels referenced to 1 micropascal per Hertz measured in the water one yard from the source), broad band frequencies (from less than 10 Hertz (Hz) to more than 190 kiloHertz (kHz)), or a high degree of signal complexity and fidelity achievable with larger and more costly underwater sound generation systems.
The need to develop reliable methods to influence the movement of marine and aquatic animals is assuming increased importance in the protection of commercially valuable and ecologically significant marine and aquatic species. Scientific, public, and legislative awareness of issues in protecting the ecology are driving requirements for mitigation of the harmful impacts of water intake, discharges, dredging, and other human activities on marine and aquatic species. Temporal mitigation is not always feasible, and mechanical barriers can be expensive to install and maintain.
It is an object of the present invention to provide a novel, effective and relative harmless method for controlling the population of marine and aquatic species in a limited area of a body of water.
It is also an object to provide such a method in Which there is monitoring of the relationship between species-specific sensitivity and the effectiveness of the stimuli employed.
Another object is to provide such a method in which there is adaptive modification and automatic change of generated sound, light, and other signals to reflect predicted and measured changes in environment and species abundance.
Still another object is to provide novel apparatus for conducting such methods and for accurately monitoring the performance of the system.
A further object is to provide such apparatus in which various combinations of stimuli may be automatically started, electronically modified, and stopped.
A still further device is to provide a practical apparatus with sufficient power and flexibility to have use in the field for protective purposes.